1. Field of the Invention
The present invention relates to a method for detecting initial magnetic pole position in permanent-magnet motor, especially to a method for detecting initial magnetic pole position in permanent-magnet motor by voltage pulse associated with motor parameters.
2. Description of Prior Art
As the progress and automation of industry, servo motors have extensive usage. For example, the CNC machine, robot arm, industrial machine, elevator and air condition generally need precise control for motor. Due to the rapid development of microprocessor and power electronics, the motor can be implemented with complex control theory to enhance the performance thereof.
The permanent magnet AC servo motor employs the pulse width modulation (PCM) signal of inverter to generate a rotational magnetic field for the stator. The rotational magnetic field for the stator is interacted with the permanent magnetic field of the rotator to produce rotational torque. In the control of permanent magnet motor, the switch of the inverter is controlled to generate suitable rotator electrical field for smooth operation of the motor. However, the initial position for the permanent magnet of the rotator is generally unknown. The rotator has both possibilities of forward and backward rotation when the motor starts. However, the uncertain in rotation direction is not desirable in certain application such as elevator. Therefore, the initial magnetic pole position in permanent-magnet motor should be precisely determined to prevent erroneous operation.
The prior art methods for determining the initial magnetic pole position in permanent-magnet motor are high frequency injection (HFI) and voltage pulse injection. The HFI method has the drawbacks of complicated calculation, priori information of d-q axis inductance, no resolution for ±180° electrical angle. The conventional voltage pulse injection method uses the principle that the current ramp slope is different for different inductance when the rotator position is different. However, the conventional voltage pulse injection method has undue dependence to motor parameters. The motor coil has risk of damage when the rising time is not correctly set. The measurement of the initial magnetic pole position is incorrect when the rising time is too low.
It is desirable to provide a fast and precise method for detecting initial magnetic pole position in permanent-magnet motor to enhance the performance and stability of the permanent-magnet motor. The method for detecting initial magnetic pole position in permanent-magnet motor is preferably less dependent on parameter and is compatible to any motor.